August 1998
LM2670
SIMPLE SWITCHER® High Efficiency 3A Step-Down
Voltage Regulator with Sync
General Description
The LM2670 series of regulators are monolithic integrated
Features
n Efficiency up to 94%
circuits which provide all of the active functions for
step-down (buck) switching regulator capable of driving up to
3A loads with excellent line and load regulation characteris-
a
n Simple and easy to design with (using off-the-shelf
external components)
n 150 mΩ DMOS output switch
n 3.3V, 5V and 12V fixed output and adjustable (1.2V to
37V ) versions
n 50µA standby current when switched OFF
>
tics. High efficiency ( 90%) is obtained through the use of a
low ON-resistance DMOS power switch. The series consists
of fixed output voltages of 3.3V, 5V and 12V and an adjust-
able output version.
±
n
2%maximum output tolerance over full line and load
The SIMPLE SWITCHER concept provides for a complete
design using a minimum number of external components.
The switching clock frequency can be provided by an inter-
nal fixed frequency oscillator (260KHz) or from an externally
provided clock in the range of 280KHz to 400Khz which al-
lows the use of physically smaller sized components. A fam-
ily of standard inductors for use with the LM2670 are avail-
conditions
n Wide input voltage range: 8V to 40V
n External Sync clock capability (280KHz to 400KHz)
n 260 KHz fixed frequency internal oscillator
n −40 to +125˚C operating junction temperature range
able from several manufacturers to greatly simplify the Applications
design process. The external Sync clock provides direct and
>
n Simple to design, high efficiency ( 90%) step-down
precise control of the output ripple frequency for consistent
filtering or frequency spectrum positioning.
switching regulators
n Efficient system pre-regulator for linear voltage
regulators
n Battery chargers
n Communications and radio equipment regulator with
synchronized clock frequency
The LM2670 series also has built in thermal shutdown, cur-
rent limiting and an ON/OFF control input that can power
down the regulator to a low 50µA quiescent current standby
±
condition. The output voltage is guaranteed to a 2% toler-
ance.
Typical Application
DS100942-3
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation
DS100942
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